The invention relates to an apparatus and to a method for determining the homogeneity of a fluid flow in a pipe.
In today's vehicles with internal combustion engines, various components for the aftertreatment of exhaust gases are provided in the exhaust strand. In the case of spark-ignition engines, these components are for example three-way catalytic converters. In diesel motors, particulate filters are usually provided nowadays to reduce the soot particulate emissions. Moreover, for example SCR catalytic converter systems or NSC systems are provided to reduce the nitrogen oxide emissions. In the SCR catalytic converter systems, an SCR (Selective Catalytic Reduction) catalytic converter is arranged in the exhaust gas region, which reduces the nitrogen oxides (NOx) contained in the exhaust gas of the internal combustion engine to nitrogen (N2) in the presence of a reducing agent. Such SCR catalytic converters are moreover used in exhaust gas systems of combustion plants, waste incineration plants, gas turbines and industrial plants.
Owing to SCR, the proportion of nitrogen oxides in the exhaust gas can be significantly reduced. For the activity of the reduction, ammonia (NH3) is required, which is admixed to the exhaust gas and reacts with the nitrogen oxides to form nitrogen and water. The reducing agents used here are NH3 or reagents which give off ammonia. In the motor vehicle sector, a 32.5% aqueous urea solution (urea-water solution; UWS) is typically used in accordance with DIN 70070, and is commercially available under the tradename AdBlue. This solution is injected into the exhaust strand upstream of the SCR catalytic converter by means of an injection system. In a hydrolysis catalytic converter arranged upstream of the SCR catalytic converter, NH3, which acts as a reducing agent, is generated from said solution. For optimum operation of the entire system, it is advantageous if the reducing agent is introduced into the catalytic converter as uniformly as possible. Introduction which is as uniform as possible in this case means as homogeneous a distribution of the reducing agent in the reducing-agent flow as possible. For this reason it is of interest to examine the reducing-agent flow and to specify a measurement method for determining the distribution of the reducing agent upstream of the catalytic converter so as to permit assessment of the functionality of the entire system.